The present invention relates to a camshaft adjuster for an internal combustion engine, wherein this camshaft adjuster is mounted on a camshaft coaxial about a camshaft axis and acts as a transmission element to a drive wheel for the rotational driving of the camshaft, and has an inner wheel arranged locked in rotation to the camshaft and an outer wheel that can rotate, and that is arranged coaxial, relative to this inner wheel, wherein at least one inner wheel vane is arranged on the inner wheel and at least one outer wheel vane is arranged on the outer wheel, wherein pressure chambers are formed between these vanes and the inner wheel vanes which define the pressure chambers with pressure chamber surfaces on the peripheral side, wherein radial boreholes are formed in the inner wheel for supplying pressurized medium to the pressure chambers.
A camshaft adjuster according to the class is already known from DE 198 17 319 C2. Camshaft adjusters of this type comprise several pressure chambers that are arranged on the periphery and that allow the inner wheel to rotate relative to the outer wheel when pressurized. For example, the phase position of the camshaft relative to the phase position of the drive wheel can be changed through pressurization. The drive wheel is driven via the crankshaft of the internal combustion engine by a traction mechanism. By adjusting the phase position of the camshaft, the control times of the intake and exhaust valves can be changed, in order to optimize the valve timing as a function of the operating point of the internal combustion engine. The inner wheel of such a camshaft adjuster has several inner wheel vanes that extend radially outward. Outer wheel vanes that point radially inward from the outer wheel extend into the intermediate spaces of the inner wheel vanes, so that the pressure chambers are formed between the vanes. Pressurized medium is fed to and discharged from the pressurized medium chambers via radial boreholes extending in the base body of the inner wheel. For controlling the pressurized medium, one control valve is provided that comprises a valve slide formed within the camshaft adjuster concentric to the camshaft axis. The valve slide is shifted axially by a central magnet arranged on the outside, in order to control the pressurization and also the depressurization of the pressure chambers. The radial boreholes extend in the radial direction from the control valve arranged centrally within the inner wheel into the pressure chambers, wherein the radial boreholes open outward from the base body of the inner wheel adjacent to the inner wheel vanes.
As an alternative to the use of a central valve, a pressurized medium distributor could be arranged within the camshaft adjuster concentric to the camshaft axis. This pressurized medium adjuster is used to guide the controlled flows of pressurized medium controlled by an external control valve that is housed, for example, in a cylinder head borehole, into the camshaft adjuster. In the case of such a design of the pressure chambers between the inner wheel and the outer wheel of a camshaft adjuster, there is the problem that the pressure chamber can be filled with pressurized medium not at all or only with difficulty, when the lateral pressure chamber surfaces of the inner wheel vanes contact the adjacent surfaces of the outer wheel vanes. In one state, this is the case in which the camshaft adjuster is located at a maximum advanced position or a maximum retarded position. In this case, a group of pressure chambers is filled completely with pressurized medium, while the other groups of pressure chambers are completely emptied. If the emptied pressure chambers are pressurized by the control valve via the radial boreholes, then an opening of the pressure chamber can be blocked for rotating the inner wheel relative to the outer wheel when the adjacent lateral pressure chamber surfaces bond to each other. The pressurized medium can be led only with difficulty between the contacting surfaces, so that the rotation of the inner wheel relative to the outer wheel is performed delayed or even blocked.